Backpack



FIG. 1 is a front perspective view of the backpack;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a right elevation view thereof;

FIG. 5 is a left elevation view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken lines showing the backpack are included for the purpose of illustrating environment and form no part of the claimed design. 

CLAIM The ornamental design for a backpack, as shown and described. 